U.S. patent application number 14/411327 was filed with the patent office on 2015-07-16 for electrosurgical resection instrument.
The applicant listed for this patent is CREO MEDICAL LIMITED. Invention is credited to Duncan Fitzsimmons, Christopher Paul Hancock, Steve Morris, Andrew Pacey, Brian Saunders, Malcolm White.
Application Number | 20150196353 14/411327 |
Document ID | / |
Family ID | 46721799 |
Filed Date | 2015-07-16 |
United States Patent
Application |
20150196353 |
Kind Code |
A1 |
Hancock; Christopher Paul ;
et al. |
July 16, 2015 |
ELECTROSURGICAL RESECTION INSTRUMENT
Abstract
An electrosurgical resection instrument for applying to
biological tissue radiofrequency electromagnetic energy has a
protective hull comprising a shaped piece of dielectric material
mounted to cover an underside of an instrument tip of the
instrument. The protective hull acts as a shield to protect tissue
that may lie under the instrument tip from damage during treatment.
The instrument may be particularly useful in procedures performed
in a gastrointestinal tract, where bowel perforation is a concern,
or in the pancreas, where damage to the portal vein or the
pancreatic duct may occur when a tumour or other abnormality is
being resected, dissected or removed.
Inventors: |
Hancock; Christopher Paul;
(Bath and North East Somerset, GB) ; Morris; Steve;
(Bath and North East Somerset, GB) ; Fitzsimmons;
Duncan; (Greater London, GB) ; Saunders; Brian;
(Hertfordshire, GB) ; Pacey; Andrew;
(Hertfordshire, GB) ; White; Malcolm;
(Monmouthshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CREO MEDICAL LIMITED |
Monmouthshire |
|
GB |
|
|
Family ID: |
46721799 |
Appl. No.: |
14/411327 |
Filed: |
June 25, 2013 |
PCT Filed: |
June 25, 2013 |
PCT NO: |
PCT/GB2013/051672 |
371 Date: |
December 24, 2014 |
Current U.S.
Class: |
606/46 |
Current CPC
Class: |
A61B 2018/1405 20130101;
A61B 18/1815 20130101; A61B 2018/128 20130101; A61B 18/1492
20130101; A61B 2018/1876 20130101; A61B 2018/00107 20130101; A61B
2018/00994 20130101; A61B 2018/1213 20130101; A61B 2018/1892
20130101; A61B 18/042 20130101; A61B 2218/002 20130101; A61B
2090/0801 20160201; A61B 2018/00494 20130101 |
International
Class: |
A61B 18/14 20060101
A61B018/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 3, 2012 |
GB |
1211776.8 |
Claims
1. An electrosurgical resection instrument for applying to
biological tissue radiofrequency (RF) electromagnetic (EM) energy,
the instrument comprising: an instrument tip comprising a planar
body made of a first dielectric material separating a first
conductive element on a first surface thereof from a second
conductive element on a second surface thereof, the second surface
facing in the opposite direction to the first surface; a coaxial
feed cable comprising an inner conductor, an outer conductor
coaxial with the inner conductor and a second dielectric material
separating the inner and outer conductors, the coaxial feed cable
being for conveying an RF signal; and a protective hull comprising
a third piece of dielectric material mounted to form the underside
of the instrument tip, wherein the inner conductor is electrically
connected to the first conductive element and the outer conductor
is electrically connected to the second conductive element to
enable the instrument tip to receive the RF signal, and
characterised in that: the first and second conductive elements
extend up to a distal side edge of the planar body to from an RF
cutting portion in which they act as active and return electrodes
to emit RF EM radiation corresponding to the RF signal from the
distal side edge of the planar body, and the protective hull has a
smoothly contoured convex undersurface facing away from the planar
body, the undersurface comprising a longitudinally extending
recessed channel formed therein between a pair of ridges.
2. An instrument according to claim 1, wherein the undersurface of
the protective hull smoothly tapers at its perimeter to meet the
side of the planar body.
3. An instrument according to claim 1, wherein the thickness of the
protective hull decreases towards the distal end of the instrument
tip.
4. An instrument according to claim 1, wherein the separation of
the first and second conductive elements at the distal side portion
edge is less than 1 mm.
5. An instrument according to claim 1, wherein the first and second
conductive elements each comprise a layers of metallisation, the
layers of metallisation being formed on opposite surfaces of the
first dielectric material.
6. An instrument according to claim 5, wherein each layer of
metallisation comprises a plated region formed from a metal having
a melting point higher than 1500.degree. C., such as titanium or
tungsten.
7. An instrument according to claim 6, wherein the first conductive
element comprises a first connecting portion between its plated
region and the inner conductor and the second conductive element
comprises a second connecting portion between its plated region and
the outer conductor, wherein the first and second connecting
portions are made from a conductive material having melting point
less than 1200.degree. C., such as silver or gold.
8. An instrument according to claim 1, wherein the protective hull
is formed from ceramic or biocompatible plastic.
9. An instrument according to claim 1, wherein the protective hull
and first dielectric material are formed in one piece as a unitary
body.
10. An instrument according to claim 1, wherein the instrument tip
has a curved distal edge.
11. An instrument according to claim 1 including a fluid feed
conduit for conveying fluid to the instrument tip for delivery out
of the instrument.
12. An instrument according to claim 11, wherein the fluid feed
conduit comprises a sleeve that defines a lumen for transporting
fluid to the instrument tip, the sleeve having the instrument tip
body and protective hull secured at a distal end thereof, and being
arranged to carry the coaxial cable in the lumen.
13. An instrument according to claim 12 including a fluid delivery
mechanism mounted at the distal end of lumen of the sleeve, the
fluid delivery mechanism being operable to deliver fluid from the
lumen through the protective hull.
14. An instrument according to claim 13, wherein the fluid delivery
mechanism includes a retractable needle mounted beneath the planar
body in the recessed channel of the protective hull.
15. An instrument according to claim 14, wherein the retractable
needle is movable in the longitudinal direction between a deployed
position in which it protrudes beyond the distal end of the
instrument tip and a retracted position in which it is set back
from the distal edge of the instrument tip.
16. An instrument according to claim 12, wherein the sleeve has
longitudinal braids therein to assist in the transfer of torque
from its proximal end to the instrument tip.
17. An instrument according to claim 12, wherein the sleeve
comprises a multi lumen tube.
18. An instrument according to claim 17, wherein the sleeve
includes an extruded separator element inserted inside a single
lumen tube, the extruded separator element including a U-shaped
channel for guiding the coaxial cable and one or more longitudinal
passages for fluid to flow along the sleeve.
19. An instrument according to claim 12, wherein the sleeve has an
outer diameter of 2.8 mm or less.
20. An instrument according to claim 12 including a cap element at
the distal end of the sleeve, the cap element covering the
electrical joint between the coaxial cable and the first and second
conductive elements.
21. An instrument according to claim 12 wherein the cap element is
formed from an impermeable insulating potting material.
22. An instrument according to claim 1, wherein the coaxial cable
is arranged to convey a microwave signal separately from or
simultaneously with the RF signal, and wherein the first and second
conductive elements are arranged on the first dielectric element to
act as an antenna to radiate microwave EM radiation corresponding
to the received microwave signal.
23. An instrument according to claim 1 for removing abnormalities,
e.g. sessile polyps, from the lower and/or upper GI tracts.
24. An instrument according to claim 1 for performing resection or
removal of tumours in close proximity to the portal vein or the
pancreatic duct.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an electrosurgical device for
delivering radiofrequency and/or microwave frequency energy into
biological tissue. In particular, the invention relates to an
electrosurgical instrument capable of delivering radiofrequency
(RF) energy for cutting tissue and/or microwave frequency energy
for haemostasis (i.e. sealing broken blood vessels by promoting
blood coagulation). The invention may be particularly suitable in
gastrointestinal (GI) procedures associated with the lower and
upper GI tract, e.g. to remove polyps on the bowel, i.e. for
endoscopic sub-mucosal resection. The invention may also lend
itself to precision endoscopic procedures, i.e. precision
endoscopic resection, and may be used in ear, nose and throat
procedures and liver resection. The device may also be used to
address procedures associated with the pancreas, e.g. to resect or
remove tumours or abnormalities in close proximity to the portal
vein or the pancreatic duct.
BACKGROUND OF THE INVENTION
[0002] Surgical resection is a means of removing sections of organs
from within the human or animal body. Such organs may be highly
vascular. When tissue is cut (divided or transected) small blood
vessels called arterioles are damaged or ruptured. Initial bleeding
is followed by a coagulation cascade where the blood is turned into
a clot in an attempt to plug the bleeding point. During an
operation, it is desirable for a patient to lose as little blood as
possible, so various devices have been developed in an attempt to
provide blood free cutting. For endoscopic procedures, it is also
undesirable for a bleed to occur and not to be dealt with as soon
as quickly as possible, or in an expedient manner, since the blood
flow may obscure the operator's vision, which may lead to the
procedure needing to be terminated and another method used instead,
e.g. open surgery.
[0003] Instead of a sharp blade, it is known to use radiofrequency
(RF) energy to cut biological tissue. The method of cutting using
RF energy operates using the principle that as an electric current
passes through a tissue matrix (aided by the ionic contents of the
cells), the impedance to the flow of electrons across the tissue
generates heat. When a pure sine wave is applied to the tissue
matrix, enough heat is generated within the cells to vaporise the
water content of the tissue. There is thus a huge rise in the
internal pressure of the cell, that cannot be controlled by the
cell membrane, resulting in the cell rupturing. When this occurs
over a wide area it can be seen that tissue has been
transected.
[0004] Whilst the above principle works elegantly in lean tissue,
it is less efficient in fatty tissue because there are fewer ionic
constituents to aid the passage of electrons. This means that the
energy required to vaporise the contents of the cells is much
greater, as the latent heat of vaporisation of fat is much greater
than that of water.
[0005] RF coagulation operates by applying a less efficient
waveform to the tissue, whereby instead of being vaporised, the
cell contents are heated to around 65.degree. C. This dries out the
tissue by desiccation and also denatures the proteins in the walls
of vessels and the collagen that makes up the cell wall. Denaturing
the proteins acts as a stimulus to the coagulation cascade, so
clotting is enhanced. At the same time the collagen in the wall is
denatured and changes from a rod like molecule to a coil, which
causes the vessel to contract and reduce in size, giving the clot
an anchor point, and a smaller area to plug.
[0006] However, RF coagulation is less efficient when fatty tissue
is present because the electrical effect is diminished. It can thus
be very difficult to seal fatty bleeders. Instead of having clean
white margins, the tissue has a blackened, burned appearance.
[0007] In practice, a RF device may operate using a waveform with a
medium crest factor that is midway between a cutting and
coagulating output.
[0008] GB 2 472 972 describes an electrosurgical instrument in the
form of a spatula comprising a planar transmission line formed from
a sheet of a first dielectric material having first and second
conductive layers on opposite surfaces thereof, the planar
transmission line being connected to a coaxial cable that is
arranged to deliver either microwave or RF energy to the planar
transmission line, the coaxial cable comprising an inner conductor,
an outer conductor coaxial with the inner conductor, and a second
dielectric material separating the outer and inner conductors, the
inner and outer conductors extending beyond the second dielectric
at a connection interface to overlap opposite surfaces of the
transmission line and electrically contact the first conductive
layer and second conductive layer respectively. The first
conductive layer is spaced from the end of the transmission line
that abuts the coaxial cable to electrically isolate the outer
conductor from the first conductive layer and also the distance of
the gap is involved with matching the impedance of the energy
delivered from the microwave source with the impedance of the
biological tissue, and the width of the first and second conductive
layers is also selected to help create an impedance match between
the transmission line and the coaxial cable.
[0009] The spatula configuration set forth in GB 2 472 972 provides
desirable insertion loss between the co-axial feed line and the end
radiating section, whilst also providing desirable return loss
properties for the edges of the spatula when in contact with air
and biological tissue respectively. In more detail, the insertion
loss along the structure may be less than 0.2 dB at the frequency
of interest, and the return loss less than (more negative than) -1
dB, preferably less than -10 dB. These properties may also indicate
a well matched junction between the coaxial cable and the
transmission line spatula structure, whereby microwave power is
launched efficiently into the spatula. Similarly, when the edges of
the spatula are exposed to air or biological tissue that is not of
interest, the return loss may be substantially zero (i.e. very
little power radiated into free space or undesirable tissue),
whereas when in contact with desirable biological tissue the return
loss may be less than (more negative than) -3 dB, preferably less
than -10 dB (i.e. the majority of power in the spatula is
transferred to the tissue).
[0010] The instrument discussed in GB 2 472 972 is intended to
radiate microwave energy from the edges of the planar transmission
line to cause localised tissue ablation or coagulation.
[0011] GB 2 472 972 also discloses that the spatula discussed above
may have an RF cutting portion integrated therewith. The RF cutting
portion may be formed by using the first and second conductive
layers mentioned above as active and return electrodes for RF
energy. This arrangement may take advantage of the fact that the
active and return electrodes are in close proximity to one another,
thus setting up a preferential return path to enable local tissue
cutting action to take place without the need for a remote return
pad or a highly conductive liquid, i.e. saline, existing between
the two electrodes.
[0012] In this example, the RF cutting portion may comprise a RF
voltage source coupled to the planar transmission line, a frequency
diplexer/duplexer unit (or signal adder) comprising a low pass
filter to prevent the high frequency microwave energy from going
back into the lower frequency RF energy source and a high pass
filter to prevent the lower frequency RF energy from going back
into the higher frequency microwave energy source. In one example,
the frequency diplexer/duplexer may be used to enable the microwave
and RF energy sources to be combined at the generator and delivered
along a single channel, e.g. co-axial cable, waveguide assembly or
twisted pair, to the spatula structure. The RF cutting energy may
be delivered alone into the tissue or it may be mixed or added with
the microwave energy and delivered simultaneously to set up a
blended mode of operation.
SUMMARY OF THE INVENTION
[0013] At its most general, the present invention provides a
development to the spatula concept discussed in GB 2 472 972 in
which the underside of the spatula includes a protective hull
comprising a shaped piece of dielectric material which overlies the
lower conductive layer and acts as a shield to protect tissue that
may lie under the spatula from damage during treatment. The
protective hull may be particularly useful in procedures performed
in the gastrointestinal tract, where bowel perforation is a
concern, or in the pancreas, where damage to the portal vein or the
pancreatic duct may occur when a tumour or other abnormality is
being resected, dissected or removed.
[0014] The protective hull may be applied to spatulas adapted for
different functions. For example, aspects of the invention
contemplated herein include: a spatula adapted to deliver
radiofrequency (RF) energy for cutting biological tissue; a spatula
adapted to deliver both RF and microwave frequency energy
separately or simultaneously; and a spatula adapted to deliver RF
and/or microwave energy and having a retractable needle for
delivering or removing fluid (liquid or gas) to or from the
treatment site. For example, the needle may be used to introduce a
gas, e.g. argon, to produce thermal or non-thermal plasma for
surface coagulation (thermal) or sterilisation (non-thermal). The
RF and/or microwave field may be used to strike and sustain or
create this plasma. The protective hull may include a passageway,
e.g. recessed channel, through which the retractable needle travels
or through which fluid can be delivered without the use of a
needle, e.g. for clinical or cleaning purposes.
[0015] According to the invention, there may be provided an
electrosurgical resection instrument for applying to biological
tissue radiofrequency (RF) electromagnetic (EM) energy, the
instrument comprising: an instrument tip comprising a planar body
made of a first dielectric material separating a first conductive
element on a first surface thereof from a second conductive element
on a second surface thereof, the second surface facing in the
opposite direction to the first surface; a coaxial feed cable
comprising an inner conductor, an outer conductor coaxial with the
inner conductor and a second dielectric material separating the
inner and outer conductors, the coaxial feed cable being for
conveying an RF signal; and a protective hull comprising a third
piece of dielectric material mounted to cover the underside of the
instrument tip, wherein the inner conductor is electrically
connected to the first conductive element and the outer conductor
is electrically connected to the second cutting element to enable
the instrument tip to receive the RF signal, wherein the first and
second conductive elements are arranged to act as active and return
electrodes to emit RF EM radiation corresponding to the RF signal
from distal side portion of the planar body, and wherein the
protective hull has a smoothly contoured convex undersurface facing
away from the planar body.
[0016] The first and second conductive elements may be arranged to
provide a local return path for RF energy, i.e. a low impedance
route for RE energy to be transported between the first and second
conductive elements. The first and second conductive elements may
be layers of metallisation formed on opposite surfaces of the first
dielectric material. The first and second conductive elements may
be arranged to set up a local electric field at a contact region in
which the instrument tip makes contact with the biological tissue.
The local electric field can be extremely high, which may cause a
microplasma (i.e. a hot thermal plasma) to be formed at the distal
side portion of the planar body, e.g. where contact is made with
the biological tissue. The microplasma may be desirable in terms of
achieving efficient cutting. The first and second conductive
elements may include portions, e.g. plated regions at and adjacent
the distal side portion, made from conductive material having a
high melting point, e.g. 1500.degree. C. or more, such as titanium,
tungsten or the like. Using such materials may prevent the high
temperatures of the microplasma from eroding the first and second
conductive elements. The first and second conductive elements may
also include connecting portions made from conductive materials
having lower melting points (e.g. silver, gold and the like)
deposited or plated on the higher melting point conductors. The
connecting portions may facilitate connection of the inner and
outer conductors of the coaxial cable, e.g. by soldering or the
like. In one embodiment, a titanium tungsten (TiW) seed layer may
be used with a layer of silver (Ag) or gold (Au) deposited on the
top. The lower melting point material may be deposited onto the
higher melting point material only in the region where the coaxial
cable inner and outer conductors are to be attached, i.e. at the
proximal end of the instrument only, and not along the sides
thereof, where the microplasma will be generated. This arrangement
follows from the fact that the electric field at the point where
the coaxial transmission line connects to the planar transmission
line should be relatively low and so the temperature at this point
should be much lower than the melting point of the lower melting
point material.
[0017] The layers of metallisation may be formed from biocompatible
materials, e.g. any of silver, titanium and gold. Table 1 below
gives the melting and boiling points for materials considered for
this device:
TABLE-US-00001 TABLE 1 Melting and Boiling Points for conductive
materials suitable for use on the instrument tip Material Melting
Point (.degree. C.) Boiling Point (.degree. C.) Tungsten (W) 3422
5555 Titanium (Ti) 1668 3287 Silver (Ag) 961.78 2162 Gold (Au)
1064.18 2856
[0018] In one embodiment, the first dielectric material separating
the conductive elements may provide the preferential return path
between the inner conductor (active) and the outer conductor
(return). RF tissue cutting may be produced at the distal side
portion of the instrument tip if the first dielectric material has
a high dielectric constant (e.g. greater than that of air) and the
thickness of the first dielectric material at the distal side
portion, i.e. the separation of the first and second conductive
elements at the distal side portion edge, is small, i.e. less than
1 mm. This arrangement may provide the necessary preferential
return path for the current to flow.
[0019] The undersurface of the protective hull may smoothly taper
at its perimeter to meet the side of the planar body. The thickness
of the protective hull may also decrease towards the distal end of
the instrument tip. Thus, the outer portion of the protective hull
may have a convex profile. The undersurface may have a
longitudinally extending recessed channel formed therein. The
tapering edge profile and recessed channel may cause the
undersurface of the protective hull to comprise a pair of ridges.
This shape may reduce the risk of the instrument digging into the
bowel wall and causing a bowel perforation or may protect the
portal vein or pancreatic duct from being damaged. The particular
dimensions of the hull (e.g. length, width, thickness, etc.) may be
adapted to suit the intended use and intended area of the body to
be operated on.
[0020] The protective hull may be formed from a biocompatible
non-conductive material, such as ceramic or biocompatible plastic
that does not stick to the wall of the bowel (or other biological
tissue) or the like. Alternatively, the hull may also be formed
from a metallic material, e.g. titanium, steel, or may be a
multi-layer structure. It may be attached (e.g. bonded) to
whichever one of the first or second conductive elements is on the
underside of the first dielectric material. However, in one
embodiment, the protective hull may be formed of the same material
as the first dielectric material. The protective hull and first
dielectric material may be formed in one piece as a unitary body.
In this arrangement one or more planar slots may be formed (e.g.
cut) in the unitary body to allow a conductive material to be
inserted to form the first and/or second conductive material.
[0021] The instrument tip may be curved at its distal end between
the side edges of the planar body. The curve may describe a
parabola in the plane of the planar body. The distal end of the
protective hull may be curved in a similar manner. This shape
prevents the instrument tip from presenting sharp corners to the
biological tissue. This shape may also enable cutting to be
performed in a direction diagonal to the long axis of the device,
in addition to cutting in the same direction or in a direction
perpendicular to the long axis.
[0022] The instrument may include a fluid feed conduit for
delivering fluid (e.g. saline) to the instrument tip. The fluid
feed conduit may comprise a passageway through the protective hull
for delivering fluid to the treatment site. The passageway may
include an outlet located in the recessed channel of the protective
hull. The fluid (liquid or gas) may be conveyed to the instrument
(protective hull) through a corresponding passageway formed within
the coaxial feed cable. The fluid feed conduit may also be used to
deliver other material to the treatment site, e.g. a gas or a solid
(e.g. powder). In one embodiment, injection of fluid (saline or the
like) is used to plump up the biological tissue at the treatment
site. This may be particularly useful where the instrument is used
to treat the wall of the bowel or the wall of the oesophagus or for
protecting the portal vein or the pancreatic duct when a tumour or
other abnormality located in close proximity, in order to protect
these structures and create a cushion of fluid. Plumping up the
tissue in this manner may help to reduce the risk of bowel
perforation, damage to the wall of the oesophagus or leakage of
from the pancreatic duct or damage to the portal vein, etc. This
aspect of the invention may make it capable of treating other
conditions where the abnormality (tumour, growth, lump, etc) is
close to a sensitive biological structure.
[0023] It is advantageous to be able to use the same instrument to
deliver fluid as delivers RF and/or microwave energy since
deflation (e.g. due to fluid seepage) may occur if a separate
instrument is introduced into the region or during treatment. The
ability to introduce fluid using the same treatment structure
enables the level to be topped up as soon as deflation occurs.
Moreover, the use of a single instrument to perform desiccation or
dissection as well as to introduce fluid also reduces the time
taken to perform the overall polyp removal procedure, reduces the
risk of causing harm to the patient and also reduces the risk of
infection. More generally, injection of fluid may be used to flush
the treatment region, e.g. to remove waste products or removed
tissue to provide better visibility when treating. As mentioned
above, this may be particularly useful in endoscopic
procedures.
[0024] The fluid feed conduit may include a needle (e.g. hypodermic
needle) mounted beneath the planar body in the recessed channel of
the protective hull. The protective hull may include a guide
passage for receiving the fluid feed conduit. The needle may have
an outer diameter less than 0.6 mm, e.g. 0.4 mm. The needle may be
movable in the longitudinal direction between a deployed position
in which it protrudes beyond the distal end of the instrument tip
and a retracted position in which it is set back from the distal
edge of the instrument tip, e.g. below the planar body or locates
proximal to the planar body. The needle may be open to fluid flow
at the proximal end or side of the needle and may be moved using
one or more control wires. For example, the proximal end of needle
may be open to the passageway formed within the coaxial feed cable.
The needle may be mounted in a through hole formed in the
protective hull. The needle may be formed an slidable interference
fit with the through hole, where it plugs the through hole to
create a fluid path of least resistance through the needle when it
is in the deployed position. This arrangement may prevent leaks
from other parts of the instrument tip. The through hole may be
formed by a tube or similar close-fit bearing surface mounted or
formed at the underside of the protective hull, e.g. in the
recessed channel.
[0025] The instrument may include a sleeve for conveying the
coaxial cable, fluid feed conduit (if present) and control wire(s)
(if present) to the instrument tip body. The instrument tip body
and protective hull may be secured (e.g. bonded) into a distal end
of the sleeve. The sleeve may include longitudinal braids to assist
in the transfer of torque from its proximal end to the instrument
tip. In one embodiment, the braided cable may be made from
Pebax.RTM. material, and may comprise a plastic outer jacket with a
metal braid attached at or to its inner wall. This type of sleeve
may provide useful torque stability, whereby a twisting force
applied to a handle attached to a proximal portion of the outer
jacket of the sleeve is transformed accurately to a rotation motion
of the instrument at the distal end of the sleeve. Preferably, the
translation between the proximal end and the distal end is one to
one (1:1), i.e. a twist of 20.degree. at the proximal end should
lead to a 20.degree. rotation of the instrument tip.
[0026] The needle is slidably movable with respect to the
protective hull through one or more control wires, which may be
actuated via a suitable slide actuator at a proximal end of the
instrument. Preferably, the needle is slidable back and forth with
respect to a fluid supply passageway which conveys the fluid to the
needle for delivery. The fluid supply passageway may be an integral
part of the sleeve, or may be a tube statically mounted in the
sleeve. The ability to move the needle back and forth while
conveying fluid to the needle through a conduit which does not move
relatively to the sleeve enables a retractable needle to be
provided within a smaller diameter sleeve than a device in which a
fluid delivery tube must slide along the length of the sleeve.
[0027] The sleeve may comprise a multi lumen tube. The lumens may
be formed by inserting an extruded separator element inside a
single lumen tube. The extruded separator element may include a
U-shaped channel for guiding the coaxial cable and one or more
through holes for carrying the fluid feed conduit and control
wire(s).
[0028] The diameter of the sleeve is preferably less than 2.8 mm to
enable it to fit down the instrument channel of an endoscope. The
handle for applying torque to the sleeve may be located at the
proximal end of the sleeve, near the endoscope controls.
[0029] The instrument may include a cap element at the distal end
of the sleeve, the cap element covering the electrical joint
between the coaxial cable and the first and second conductive
elements. The cap element may be formed from a heat shrink material
or from potting adhesive. Protecting the joint in this way may
prevent arcing from occurring at the electrical joint during use.
In particular, the cap element is arranged to seal the distal
electrical connections from fluid at the instrument tip. Ingress of
fluid to the junction where the co-axial cable is connected to the
parallel plate planar transmission line is undesirable, as either
the microwave energy may be absorbed, which will lead to heating
and the energy not being delivered along the edge of the blade in
an efficient manner, or the device will breakdown or flashover due
to the lower breakdown voltage. The potting adhesive may comprises
a combination of glues, e.g. low viscosity and high viscosity UV
curing medically approved glues may be used such as Loctite.RTM.
4304 or Loctite.RTM. 4305, the low viscosity adhesive being useful
for filling gaps, and the low viscosity being useful for wicking
the adhesive into very fine potential fluid paths.
[0030] The instrument tip may also be arranged to receive microwave
frequency energy. The coaxial cable may be arranged to convey a
microwave signal separately from or simultaneously with the RF
signal. The first and second conductive elements may be arranged on
the first dielectric element to act as a near field antenna to
radiate microwave EM radiation corresponding to the received
microwave signal.
[0031] This embodiment may make use of the ability of the
instrument to be "seen" differently by the RF signal and microwave
signal. For the RF signal, the instrument tip may be modelled as a
parallel plate capacitor. The electric field set up by the RF
signal between the first and second conductive elements can be
substantially contained with the planar body (first dielectric
material) by setting the edges of the first and second conductive
layers back from the side edges of the planar body. To perform RF
cutting, it is desirable for the field to extend outside the planar
body. In this invention it is possible to do this be extending the
edges of the first and second conductive layers up to the side edge
of the planar body in a region designated as an RF cutting portion.
The RF field set-up between the two plates of the parallel plate
capacitor (or planar transmission line) and coupled into the
biological tissue, through making contact with one or more edges of
the blade, may create a controlled microplasma and the microplasma
may enable or enhance the tissue cutting process.
[0032] Meanwhile, for the microwave signal, the instrument tip may
be modelled as a parallel plate transmission line with the planar
body representing dielectric material separating two conductive
plates. The radiation pattern of the microwave frequency EM energy
in this case depends on the overall shape of the planar body and
the microwave feed structure. In this particular instance, the gap
at the proximal end between the co-axial feed line (centre
conductor) and the upper conductive layer plays an important role
in ensuring that the microwave energy from the source is matched in
terms of impedance with the load impedance presented by the tissue.
The overall length of the planar transmission line arrangement is
also important in terms of matching the impedance (or the energy
delivery) of (or from) the coaxial transmission line with (or into)
the biological tissue, i.e. the structure may form a quarter wave
impedance transformer or a half wavelength resonator. Using known
simulation tools, this may be modelled to control from which edges
the microwave frequency EM energy is radiated. For example, the
instrument tip may be configured to inhibit radiation of the
microwave EM radiation from a distal edge of the planar body.
[0033] Herein, radiofrequency (RF) may mean a stable fixed
frequency in the range 10 kHz to 300 MHz and microwave frequency
may mean a stable fixed frequency in the range 300 MHz to 100 GHz.
The RF energy should have a frequency high enough to prevent the
energy from causing nerve stimulation and low enough to prevent the
energy from causing tissue blanching or unnecessary thermal margin
or damage to the tissue structure. Preferred spot frequencies for
the RF energy include any one or more of: 100 kHz, 250 kHz, 400
kHz, 500 kHz, 1 MHz, 5 MHz. Preferred spot frequencies for the
microwave energy include 915 MHz, 2.45 GHz, 5.8 GHz, 14.5 GHz, 24
GHz.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Embodiments of the invention are discussed in detail below
with reference to the accompanying drawings, in which:
[0035] FIG. 1 is a partly transparent perspective view of an
electrosurgical instrument that is an embodiment of the
invention;
[0036] FIG. 2 is a front view of the instrument of FIG. 1;
[0037] FIG. 3 is a top view of the instrument of FIG. 1;
[0038] FIG. 4 is a side view of the instrument of FIG. 1;
[0039] FIG. 5 is a cross-sectional side view through the instrument
of FIG. 1;
[0040] FIG. 6 is perspective view of the radiating section and
retractable needle of an electrosurgical instrument according to
the invention showing the needle in a deployed configuration;
[0041] FIG. 7 is a perspective view of the radiating section and
retractable needle of FIG. 6 showing the needle in a retracted
configuration;
[0042] FIG. 7A is a cross-sectional view of the retractable needle
mounted in the instrument;
[0043] FIG. 8 is a perspective view of the end of an
electrosurgical instrument according to an embodiment of the
invention;
[0044] FIG. 9 is a cross-section side view through the instrument
shown in FIG. 8;
[0045] FIG. 10 is a cross-section view through the shaft of an
electrosurgical instrument according to one embodiment of the
invention;
[0046] FIG. 11 is a cross-section view through the shaft of an
electrosurgical instrument according to another embodiment of the
invention;
[0047] FIGS. 12A and 12B are perspective front and rear views
respectively of a protective hull member suitable for use with the
present invention;
[0048] FIGS. 13 to 16 illustrate how the length of the spatula may
be adapted as its end is curved;
[0049] FIGS. 17 to 20 show views of a simulation configuration for
a spatula with differing gaps between the top conductor of the
spatula and the coaxial feed; and
[0050] FIGS. 21 to 23 are graphs showing the return loss for
spatulas having different gaps between the top conductor of the
spatula and the coaxial feed.
DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES
[0051] An electrosurgical instrument 100 that is an embodiment of
the invention is now described with reference to FIGS. 1 to 9. The
instrument comprises a sleeve 102 having an instrument tip 104
connected at its distal end. The sleeve 102 is made from a flexible
polymer material (e.g. Pebax.RTM.) having axially-extending braids
(e.g. of metal) encapsulating within it. This arrangement forms a
torque stable system. The braids may not extend right up to the
distal end of the sleeve, thus introducing a safe distance (e.g. of
no less than 1 mm as measured along the longitudinal axis between
the end of the braid and the proximal edge of the instrument tip in
order to avoid any risk of heating of the braid as a result of
capacitive conductance during use of microwave energy. A sleeve
without braid may extend across this safe distance gap. This
arrangement also prevents the two plates of the planar transmission
line or the two conductors in the co-axial transmission line from
becoming shorted or connected together. The braid structure enables
torque applied to the proximal end of the sleeve to be accurately
transformed into rotational movement of the instrument tip 104. For
convenience, the sleeve 102 is shown as transparent in the drawings
to permit illustration of its internal components. In practical
embodiments, the sleeve may be opaque.
[0052] The instrument tip 104 comprises a dielectric block 106 that
has layers of metallisation 105, 107 on its upper and lower
surfaces. The layers of metallisation correspond to the first and
second conductive elements of the invention. The layers of
metallisation are separated by the thickness of the dielectric
block 106 to form a bipolar radiating spatula structure, similar to
that disclosed in GB 2 472 972.
[0053] The layers of metallisation may be formed from high melting
point conductors, e.g. W or Ti. In such an arrangement, lower
melting point conductors may be deposited around the regions where
the coaxial cable connects to the parallel plate planar
transmission line to facilitate soldering the coaxial arrangement
to the planar transmission line. The lower melting point conductors
may be silver (Ag) or gold (Au).
[0054] As seen most clearly in FIG. 2, the distal end of the
dielectric block is formed in a curved, e.g. parabolic, shape. This
shape is preferred so that the instrument does not present sharp
corners at its outer edges, and to enable use in multiple
directions of travel. Such sharp corners can be undesirable when
the instrument is used in environments with delicate tissue
structures, such as the gastrointestinal tract, where the bowel
wall is very thin.
[0055] The sleeve 102 defines a lumen which carries a flexible
coaxial feed cable 108 and a fluid delivery structure. In this
embodiment, the fluid delivery structure includes a passageway
formed by space in the lumen around the flexible feed cable 108 and
a retractable needle 110. The sleeve 102 carries a control wire 112
for both deploying and retracting the needle 110. Operation of the
needle is described below.
[0056] The inner conductor 114 of the coaxial feed cable 108
protrudes from the distal end of the coaxial feed cable 108 and is
electrically bonded (e.g. using solder) to the upper layer 105 of
metallisation (first conductive element). The outer conductor of
the coaxial cable 116 is electrically coupled to the lower layer of
metallisation 107 (second conductive element) by a braid
termination 118. The braid termination 118 comprises a tubular part
that is electrically bonded to the outer conductor and a distally
extending plate part 109 that fits under the dielectric block 106
and is electrically connected to the lower layer 107 of
metallisation.
[0057] In this embodiment, a shaped piece of dielectric material
120 is attached to the lower surface of the dielectric block 106.
It may be secured to the lower layer 107 of metallisation. The
underside of the shaped piece of dielectric material 120 has a
configuration particularly suited for use in procedures performed
in the gastrointestinal tract. In the longitudinal direction, the
shaped piece of dielectric material 120 comprises a distal part
which gradually tapers (e.g. in a curved manner) towards the
dielectric block 106. This part of the instrument is in closest
proximity to the tissue being treated in use, e.g. the bowel wall,
the wall of the oesophagus, the portal vein, or the pancreatic
duct. By presenting a curved surface in this way, unwanted
perforation of the bowel wall or the wall of the oesophagus or
damage to the portal vein or the pancreatic duct can be
avoided.
[0058] As can be seen most clearly in FIG. 2, the undersurface of
the shaped piece of dielectric material 120 has a longitudinally
extending recessed channel 122. The recessed channel defines an
access path for the retractable needle 110. The recessed nature of
the channel means that the access path is flanked one both sides by
longitudinally extending ridges 124 of the shaped piece of
dielectric material.
[0059] The surface of the shaped piece of dielectric material 120
that engages with the underside of the radiating spatula structure
is shown in more detail in FIGS. 12A and 12B. The distal end of the
shaped piece of dielectric material 120 has a flat upper surface
126 for contacting the lower layer of metallisation 107. A
rectangular recess 129 is formed towards the proximal end of the
flat upper surface 126 for receiving the plate part 109 of the
braid termination 118.
[0060] The proximal end of the shaped piece of dielectric material
120 is formed with a U-shaped channel 128 for receiving and
supporting the distal end of the coaxial feed cable 108. FIG. 12B
shows that a similar channel 130 is formed on the underside of the
proximal end of the shaped piece of dielectric material 120 to
receive a guide conduit for the retractable needle (see FIGS. 6 and
7). The outer surface of the proximal end of the shaped piece of
dielectric material 120 is cylindrical, with a diameter selected to
fit inside the sleeve.
[0061] At the sides of the shaped piece of dielectric material 120
between the proximal and distal ends, there are a pair of
upstanding wing portions 132, whose inner surfaces engage with
respective side edges of the radiating spatula structure and whose
outer surface engage in an interference fit with the inner surface
of the sleeve 102.
[0062] The shaped piece of dielectric material 120 is preferably
made from a ceramic or other material having low thermal
conductivity.
[0063] In another embodiment, the dielectric body 106 and the
shaped piece of dielectric 120 may be formed in one piece, i.e. as
a unitary body. The unitary body may have a planar slot formed
(e.g. cut) therein for receiving a conductive material to form the
lower layer of metallisation (second conductive element). The
thickness of the slot and therefore the lower layer of
metallisation may be 0.1 mm or more, but preferably no more than
0.2 mm.
[0064] The overall size of the instrument may be such that it is
suitable for insertion through the instrument channel of an
endoscope. Thus, the outer diameter of the sleeve may be 2.8 mm or
less, e.g. 2.7 mm.
[0065] FIGS. 6, 7, and 7A illustrate operation of a control wire
138 for deploying and retracting a retractable needle 136. The
sleeve 102 and shaped piece of dielectric material 120 are omitted
in FIGS. 6 and 7 for clarity. The retractable needle 136 is
slidably mounted in a needle sleeve 134, which is fixed in the
channel 130 formed in the underside of the shaped piece of
dielectric material 120. The retractable needle 136 is capable for
sliding between a deployed position (shown in FIG. 6), where it
protrudes from the distal end of the instrument, and a retracted
position (shown in FIG. 7) where the distal end of the needle is
set back from the distal end of the instrument. The retractable
needle 136 is attached at the end of a needle base unit 140, which
is itself slidable within the sleeve by operating (i.e. pushing or
pulling as appropriate) a suitable control wire 138, as is
conventional. The control wire 138 is preferably welded in-line
with the needle 138 as shown in FIGS. 6 and 7, as this allows a
more compact arrangement. Alternatively, the control wire may abut
against a side surface of the needle or needle base unit, as shown
in FIG. 1.
[0066] When the control wire 138 pushes the needle 136 to its
forward-most (i.e. deployed) position the needle base unit 140
abuts the needle sleeve to create a seal. The needle base unit 140
prevents the needle from being pushed too far out of the
instrument. As shown in FIG. 7A, the space 139 in the lumen outside
the coaxial cable 108 and retractable needle 136 forms a passageway
for carrying fluid from the proximal end of the sleeve, where for
example it may be injected by a user. An aperture 143 (seen in FIG.
7a) formed in a side wall of the needle base unit 140 provides a
fluid flow path between the space 139 in the lumen and the proximal
end of the needle 136. This enables fluid that has travelled down
the length of the fluid conduit within the sleeve 102 to access the
proximal end of the needle and be injected out through the needle
tip.
[0067] As shown in FIG. 7A, the control wire slides in a guide
conduit 141, which can prevent buckling of the control wire when it
is under compression, thereby improving accuracy of control over
the needles position. The guide conduit 141 may be formed in a
semi-rigid insert mounted in the sleeve, as discussed below with
reference to FIGS. 10 and 11.
[0068] In the retracted position, the distal end of the needle 136
(i.e. the needle tip) may be enclosed by the needle sleeve 134 to
prevent accidental snagging on either patient tissue or the
internal structure of an endoscope. The needle 136 may be a
hypodermic needle terminating with a sharp point for penetrating
biological tissue.
[0069] Injection of fluid (saline or the like) to plump up or raise
the biological tissue may be particularly useful where the
instrument is to treat the wall of the bowel or the wall of the
oesophagus. For example, the instrument may be particular useful
for removing sessile polyps, which sit flat on the wall of the
bowel. Plumping up the tissue in this manner may help to reduce
risk of bowel or oesophagus perforation. It is advantageous to be
able to use the same instrument to deliver fluid as delivers RF
and/or microwave energy since deflation (e.g. due to fluid seepage)
may occur if a separate instrument is introduced into the region or
during treatment. The ability to introduce fluid using the same
treatment structure enables the level to be topped up as soon as
deflation occurs. Moreover, the use of a single instrument to
perform desiccation or dissection as well as to introduce fluid
also reduces the time taken to perform the polyp removal procedure,
reduces the risk of causing harm to the patient and also reduces
the risk of infection. More generally, injection of fluid may be
used to flush the treatment region, e.g. to remove waste products
or removed tissue to provide better visibility when treating. This
may be particularly useful in endoscopic procedures.
[0070] FIG. 8 shows a view of the instrument tip, in which the
distal end of the sleeve 102 is "potted" in a cap element 142,
which covers the electrical joint between the radiating spatula
structure and the coaxial cable. The cap element 142 may be formed
from a suitable a heat shrink material or from potting adhesive,
e.g. UV curable adhesive such as Loctite.RTM. 4304 and/or
Loctite.RTM. 4305. Protecting the joint in this way may prevent
arcing from occurring at the electrical joint during use. The
adhesive used should not be lossy or absorb energy at the microwave
frequency of choice. Using a small amount of adhesive will also
minimise the amount of energy coupled into it. If microwave power
is absorbed by the adhesive, it will cause local heating and loss
of microwave power available at the edges of the blade.
[0071] FIG. 9 shows a schematic cross-section view of the distal
end of the instrument. In this view the needle 136 is deployed.
Here the distal end of the sleeve 102 includes a widened portion
144 having an increased diameter. The widened portion 144 provides
more space at the distal end, which gives more room for the needle
deployment mechanism and a more robust connection between the
coaxial cable 108, radiating spatula structure 105, 106, 107 and
shaped piece of dielectric material 120.
[0072] FIG. 10 shows a cross-section view through the sleeve 102
facing towards the distal end of the instrument. Mounted within the
sleeve 102 is a semi-rigid insert 146 that is arranged to maintain
the position of the coaxial cable 108 and push wire 112 along the
length of the sleeve 102. The insert 146 may be a length of
extruded plastic material or the like. In FIG. 10 the insert 146
has a horse-shoe shaped cross-section, with an outer surface for
engaging the inner surface of the sleeve, and a U-shaped channel
for receiving the coaxial cable 108. Two longitudinally extending
circular passages are formed within the insert for carrying the
push wire and for providing space for a fluid path respectively.
Maintaining the position of the push wire is important, because if
movement of the push wire is unconstrained within the lumen of the
sleeve, control of the wire can be lost e.g. due to the push wire
moving laterally within the sleeve.
[0073] Although shown as a separate insert in this embodiment,
these passages may be incorporated into the sleeve itself, e.g. as
a single extrusion or through bonding or welding to the inner
surface of the sleeve 102. The insert may exhibit lateral strength
to provide crush resistance and durability to the device.
[0074] FIG. 11 shows a similar view to FIG. 10 for another extruded
rigid insert 148. The effect of the semi-rigid inserts 146, 148 is
to provide multiple lumens within a common sleeve 102.
[0075] When used to deliver microwave frequency energy, the
radiating spatula behaves as a resonant microwave structure, fed
from a coaxial transmission line. Its function is to pass microwave
energy into biological tissue that is close to or touching the
region near the tip of the spatula. As mentioned above, the distal
end of the radiating spatula blade is curved to avoid presenting
sharp edges or corners to tissue in use. A discussion of the effect
of changing the shape of the end of the spatula on the delivery of
microwave energy is presented below with reference to FIGS. 13 to
23.
[0076] The spatula is a low impedance planar transmission line,
that is to say that the ratio of the voltage between the top and
bottom metal plates to the (equal and opposite) currents in the two
plates is close to 30.OMEGA. (calculated using microwave field
modelling software). Typically, the transmission line feeding the
spatula has an impedance of 50.OMEGA.. Thus, the transmission line
and the biological tissue touching the end of the spatula appear as
high impedances to the spatula.
[0077] The difference in impedance at each end would normally
present a partial obstacle to the passage of power into and out of
the spatula. However, when the spatula is close to a whole number
of half-wavelengths long, the voltages at the end of the spatula
increase, and the currents at the end decrease, both due to a
resonant effect, so that power passes readily from the coaxial line
through the spatula into the tissue. For this reason the length of
the spatula, from the end of the coaxial transmission line to the
other end of the spatula (or planar transmission line), plays a
significant role in the effectiveness of the spatula.
[0078] The length of the spatula is carefully adjusted so that,
taking into account the modification of the wavelength by the shape
of the spatula, the dielectric constant of the material between the
plates, and fringing fields at each end of the spatula, the spatula
is close to one half wavelength long at the operating frequency. In
practice this length can be found empirically by numerical
simulation and/or experiment.
[0079] The effect of changes in shape in the end of the spatula can
be understood in terms of a change in the capacitance of the end of
the spatula.
[0080] Under resonant conditions, the centre of the rectangular
spatula shown in FIG. 13 behaves in a similar way to an electrical
inductance (coil) and each end behaves similarly to a capacitor, as
shown schematically in FIG. 14. The product of the capacitance and
the inductance is proportional to the inverse square of the
frequency at which the spatula will resonate. This is described by
the standard electrical relation
f = 1 2 .pi. LC ##EQU00001##
for the resonant frequency f of a resonant electrical circuit with
a capacitance C and an inductance L.
[0081] If the shape of the end of the spatula is changed, this
results in a change in capacitance so that the resonant frequency
of the spatula changes, or to put it another way the spatula is now
not the correct length to resonate at the operating frequency.
[0082] The overall length of the spatula can, however, be adjusted
to bring it back into resonance. A good approximation to the length
adjustment needed is that required to return the area of the
spatula to the value before the end was rounded--this is equivalent
to adjusting the capacitance back to its previous value.
[0083] Capacitance is proportional to the area of the capacitor. If
the end of the spatula were rounded off to a semi-circle or
ellipse, then the length should be increased so that the extra
rectangular part has the same area as the parts cut off to make the
semi-circular end, as indicated in FIG. 15.
[0084] The missing area in FIG. 15 is
2 r 1 r 2 - .pi. r 1 f 2 2 .apprxeq. 2 r 1 .times. 0.2146 r 2
##EQU00002##
[0085] where r.sub.1 is half the width of the spatula and r.sub.2
is the half-length of the ellipse that forms the curved end.
[0086] The area of the rectangle to be added shown in FIG. 16
is
2r.sub.1x=2r.sub.1.times.0.2146r.sub.2
[0087] where x is the extra length required.
[0088] Thus the extra length required is approximately 0.215 times
the length of the rounded part of the spatula. If the rounded end
is 3 mm long, the extra length required is about 0.64 mm. This
increase in length was tested by simulation with the actual shape
of the spatula and found to be close to the optimum. The length of
the model was adjusted empirically to find the optimum, which was
actually 0.6 mm.
[0089] The change in resonant frequency may also be corrected by
changing the capacitance of the other end of the spatula, by
changing the geometry of the connection to the 50.OMEGA. coaxial
cable. A simple way to do this is to change the spacing between the
top plate of the spatula and the coaxial line.
[0090] The general shape of the spatula is shown in FIG. 17, and a
side view of the spatula with 0.4 mm gap is shown in FIG. 18. A
side view of the spatula with 0.1 mm gap is shown in FIG. 19, and a
close up side view in FIG. 20.
[0091] In FIG. 20, the gap between the top plate of the spatula and
the coaxial line forms a capacitor that can be used to adjust the
resonant frequency of the spatula. If the gap is reduced, the
capacitance increases, and the resonant frequency drops.
[0092] FIG. 21 shows the return loss for the 10.6 mm long spatula
with a 0.4 mm gap. The best return loss is close to 5.8 GHz.
[0093] FIGS. 22 and 23 compare the return loss for a 10 mm long
spatula with 0.3 mm and 0.1 mm gaps respectively. It can be seen in
FIG. 22 that with the 0.3 mm gap the best return loss is at 6 GHz,
and in FIG. 23 with a 0.1 mm gap the best return loss is close to
5.8 GHz.
[0094] It may be difficult to accurately manufacture the device
with a 0.1 mm gap, so the solution of increasing the spatula length
to adjust for changing the overall shape may be preferred. However,
other ways of increasing the capacitance at the cable end of the
spatula might be used, such as increasing the thickness of the top
plate, which may happen anyway when solder is applied.
[0095] Because it may be difficult to accurately describe the
geometry that is actually achieved around the connection between
the cable and the spatula, the best approach is to aim for a
geometry that is easily built and is repeatable.
* * * * *